1. Field of Invention
The present invention relates to a vehicle height adjust control apparatus and method for adjusting an actual vehicle height to a predetermined target vehicle height.
2. Description of Related Art
A vehicle height adjust control apparatus as described in, for example, Japanese Patent Application Laid-Open No. HEI 2-3515, includes actuators capable of changing a vehicle height, and a vehicle height detection device for detecting the vehicle height. The apparatus performs vehicle height adjust control by integrating the amount of shift of the detected vehicle height from a predetermined target vehicle height and, when the integral of the amount of shift exceeds a predetermined value, controls the actuators so that the detected vehicle height becomes equal to the target vehicle height. This manner of control avoids starting a vehicle height adjusting operation in response to a temporary vehicle height change, thereby preventing unnecessary vehicle height adjustment.
Japanese Patent Application Laid-Open No. SHO 62-0241716 describes a technology wherein the detected vehicle height sampling time is reduced when a detected vehicle height is out of an allowable range around a target vehicle height, in comparison with a case where the detected vehicle height is within the allowable range. This prevents overshoot of the vehicle height resulting from a delay of the vehicle height detection during vehicle height adjustment and also prevents unnecessary performing of vehicle height adjusting operations due to an excessively high sensitivity in the vehicle height detection.
However, these conventional apparatus do not consider either the vehicle height changes while the vehicle is stopped or the difference between the vehicle height changing rate during the vehicle body raising control and the vehicle height changing rate during the vehicle body lowering control, and therefore suffer from several problems. That is, if the vehicle is stopped with the engine turned off, there is a high possibility of a vehicle height change due to a change in the baggage weight on the vehicle, or a high possibility of a vehicle height reduction due to a temperature reduction of fluid in an apparatus wherein hydraulic actuators and the like are used. Considering such circumstances, it is desirable to adjust the vehicle height to a target vehicle height more quickly at the time of starting the engine than during the running of the vehicle, If it is determined whether to start vehicle height adjustment on the basis of the integral of the amount of shift of the vehicle height as in the aforementioned conventional apparatus, it requires an undesirably long time to start the vehicle height adjustment during an initial period following starting of the engine.
Additionally, the vehicle body is raised against the vehicle's own weight by operating the actuators, whereas the vehicle body can be lowered by using the vehicle's own weight. Therefore, the vehicle height changing rate becomes greater when the vehicle height is being reduced than when the vehicle height is being increased. Consequently, vehicle height adjust control apparatus that do not consider the vehicle height changing rate as in the aforementioned apparatus have a problem as there is a high possibility of downward overshoot of the vehicle body during the lowering control of the vehicle body.